Hannah Wilber writes...
"If you’ve spent any time in the ArcGIS StoryMaps builder, you know the block palette is at the heart of the authoring experience. Whether you’re adding text, a YouTube video, a map, or something else, it all starts right there. But not all blocks are created equal. There are some special, immersive blocks that go the extra mile when it comes to engaging your readers.."
Read more at Slideshow (beta): A new immersive block in ArcGIS StoryMaps